scholarly journals MICROTUBULE BIOGENESIS AND CELL SHAPE IN OCHROMONAS

1973 ◽  
Vol 56 (2) ◽  
pp. 360-378 ◽  
Author(s):  
David L. Brown ◽  
G. Benjamin Bouck
Keyword(s):  
Cell Shape ◽  
Preceding Paper ◽  
Cell Organelles ◽  
Site Function ◽  
Specific Shape ◽  
Cytoplasmic Microtubules ◽  
Normal Shape ◽  
Species Specific ◽  
Anterior Direction ◽  
Made In

The proposal made in the preceding paper that the species-specific shape of Ochromonas is mediated by cytoplasmic microtubules which are related to two nucleating sites has been experimentally verified. Exposure of cells to colchicine or hydrostatic pressure causes microtubule disassembly and a correlative loss of cell shape in a posterior to anterior direction. Upon removal of colchicine or release of pressure, cell shape regenerates and microtubules reappear, first in association with the kineto-beak site concomitant with regeneration of the anterior asymmetry, and later at the rhizoplast site concomitant with formation of the posterior tail. It is concluded that two separate sets of cytoplasmic tubules function in formation and maintenance of specific portions of the total cell shape. On the basis of the following observations, we further suggest that the beak and rhizoplast sites could exert control over the position and timing of the appearance, the orientation, and the pattern of microtubule distribution in Ochromonas. (a) the two sites are accurately positioned in the cell relative to other cell organelles; (b) in regenerating cells microtubules reform first at these sites and appear to elongate to the cell posterior; (c) microtubules initially reappear in the orientation characteristic of the fully differentiated cell; (d) the two sets of tubules are polymerized at different times, in the same sequence, during reassembly or resynthesis of the microtubular system. Experiments using cycloheximide, after a treatment with colchicine, have demonstrated that Ochromonas cannot reassume its normal shape without new protein synthesis. This suggests that microtubule protein once exposed to colchicine cannot be reassembled into microtubules. Pressure-treated cells, on the other hand, reassemble tubules and regenerate the normal shape in the presence or absence of cycloheximide. The use of these two agents in analyzing nucleating site function and the independent processes of synthesis and assembly of microtubules is discussed.

scholarly journals MICROTUBULES IN THE FORMATION AND DEVELOPMENT OF THE PRIMARY MESENCHYME IN ARBACIA PUNCTULATA

1969 ◽  
Vol 41 (1) ◽  
pp. 227-250 ◽  
Author(s):  
Lewis G. Tilney ◽  
John R. Gibbins
Keyword(s):  
Hydrostatic Pressure ◽  
Sea Urchin ◽  
Cell Shape ◽  
Preceding Paper ◽  
Careful Analysis ◽  
The Other ◽  
Arbacia Punctulata ◽  
Cell Form ◽  
Cytoplasmic Microtubules ◽  
Made In

To experimentally test the suggestion made in the preceding paper that the microtubules are involved in cell shape development during the formation and differentiation of the primary mesenchyme, we applied to the embryos two types of agents which affect cytoplasmic microtubules: (a) colchicine and hydrostatic pressure, which cause the microtubules to disassemble, and (b) D2O, which tends to stabilize them. When the first type of agent is applied to sea urchin gastrulae, the development of the primary mesenchyme ceases, the microtubules disappear, and the cells tend to spherulate. With D2O development also ceases, but the tubules appear "frozen," and the cell asymmetries persist unaltered. These agents appear to block development by primarily interfering with the sequential disassembly and/or reassembly of microtubules into new patterns. The microtubules, therefore, appear to be influential in the development of cell form. On the other hand through a careful analysis of the action of these agents and others on both intra- and extracellular factors, we concluded that the microtubules do rather little for the maintenance of cell shape in differentiated tissues.

The role of microtubules in chick blastoderm expansion—a quantitative study using colchicine

Development ◽  
1975 ◽  
Vol 34 (1) ◽  
pp. 265-277
Author(s):  
J. R. Downie
Keyword(s):  
Cell Division ◽  
Cell Shape ◽  
Shape Change ◽  
Cell Sheet ◽  
Cell Movement ◽  
Vitelline Membrane ◽  
General Context ◽  
Chick Blastoderm ◽  
Cell Shape Change ◽  
Cytoplasmic Microtubules

Since their discovery, cytoplasmic microtubules have been much studied in the context of cell movement and cell shape change. Much of the work has used drugs, particularly colchicine and its relatives, which break down microtubules — the so-called anti-tubulins. Colchicine inhibits the orientated movements of many cell types in vitro, and disrupts cell shape change in several morphogenetic situations. The investigation reported here used chick blastoderm expansion in New culture in an attempt to quantify the colchicine effect on orientated cell movement. However, although colchicine could halt blastoderm expansion entirely, a simple interpretation was not possible. (1) Colchicine at concentrations capable of blocking mitosis, and of disrupting all or most of the cytoplasmic microtubules of the cells studied, inhibited blastoderm expansion, often resulting in an overall retraction of the cell sheet. (2) Though blastoderm expansion does normally involve considerable cell proliferation, the colchicine effect could not be ascribed to a block on cell division since aminopterin, which stops cell division without affecting microtubules, did not inhibit expansion. (3) Blastoderm expansion is effected by the locomotion of a specialized band of edge cells at the blastoderm periphery. These are the only cells normally attached to the vitelline membrane — the substrate for expansion. When most of the blastoderm was excised, leaving the band of edge cells, and the cultures then treated with colchicine, expansion occurred normally. The colchicine effect on blastoderm expansion could not therefore be ascribed to a direct effect on the edge cells. (4) An alternative site of action of the drug is the remaining cells of the blastoderm. These normally become progressively flatter as expansion proceeds. If flattening in these cells is even partially dependent on their cytoplasmic microtubules, disruption of these microtubules might result in the inherent contractility of the cells resisting and eventually halting edge cell migration. That cell shape in these cells is dependent on microtubules was demonstrated by treating flat blastoderm fragments with colchicine. On incubation, the area occupied by these fragments decreased by 25–30 % more than controls. The significance of these results in the general context of orientated cell movements and cell shape determination is discussed, with particular emphasis on the analogous system of Fundulus epiboly.

scholarly journals Glucose-6-phosphate-dehydrogenase-deficient erythrocytes have an impaired shape recovery mechanism

Blood ◽  
1984 ◽  
Vol 63 (5) ◽  
pp. 1198-1202
Author(s):  
E Alhanaty ◽  
M Snyder ◽  
MP Sheetz
Keyword(s):  
Cell Shape ◽  
Shape Recovery ◽  
Cell Function ◽  
Hexose Monophosphate ◽  
Recovery Rates ◽  
Chloromethyl Ketone ◽  
Hexose Monophosphate Shunt ◽  
Recovery Mechanism ◽  
Normal Shape ◽  
Glucose 6 Phosphate Dehydrogenase

In the human erythrocyte, the maintenance of the biconcave disc shape is important for cell viability as well as cell function. Previous studies have indicated the involvement of the hexose monophosphate shunt in the recovery of discoid shape after perturbation of echinocytic agents. In glucose-6-phosphate-dehydrogenase-deficient (Gd- ) erythrocytes, the shunt activity is significantly decreased; thus, it might be expected that the shape recovery rate of Gd- erythrocytes would be decreased. We show here that shape recovery rates in the presence of the shunt stimulator methylene blue are as much as fivefold lower in Gd- erythrocytes. We also show that the protease inhibitor, N- alpha-tosyl-1-phenylalanine-chloromethyl ketone, has no effect on shape recovery in Gd-, whereas it increases normal cell shape recovery rates by 10–30-fold at 50 microM and causes cupping at 200 microM (see companion article by Alhanaty et al.). These changes are not due to reticulocytosis, as other hemolytic disorders do not show such changes. Further, both chronic hemolyzing Gd and A Gd variants show similar abnormal shape recovery behavior, whereas the extent of hemolysis is quite different between variants. Thus, the activity of the hexose monophosphate shunt appears to have a dramatic effect on the rate of reversal of echinocytosis. The lack of shunt activity of Gd cells would necessarily impair their ability to recover normal shape after perturbation.

Transport of Food Through the Alimentary Camals of Aquatic Annelids

1948 ◽  
Vol s3-89 (5) ◽  
pp. 47-51
Author(s):  
JEAN HANSON
Keyword(s):  
Alimentary Canal ◽  
Anterior Part ◽  
Gut Contents ◽  
Ciliated Epithelium ◽  
Gut Epithelium ◽  
The University ◽  
Anterior Direction ◽  
Metachronal Waves ◽  
Muscle Coat ◽  
Made In

1. In most serpulids and sabellids the only muscle coat in the wall of the alimentary canal lies outside the blood sinus which envelops it. In a few sabellids there is another muscle coat, of unknown function, between the sinus and the gut epithelium. 2. The muscles outside the sinus contract antiperistaltically and tend to hinder the transport of the gut contents towards the anus. 3. The contents of the alimentary canal are transported by its cilia which beat towards the anus. The metachronal waves of the ciliated epithelium travel in a postero-anterior direction. The ‘ascending ciliary current’ of Stephenson (1913) does not exist. 4. The food boli of serpulids and sabellids rotate as they move down the gut. In Salmacina incrustans the rotation is imparted by cilia in the anterior part of the gut. These observations were made in the Zoological Station of Naples. I wish to record my gratitude to the staff of the Station, to the British Association for the Advancement of Science for the use of its Table, and to the University of London for a grant towards travelling expenses.

scholarly journals byr2, a Schizosaccharomyces pombe gene encoding a protein kinase capable of partial suppression of the ras1 mutant phenotype.

1991 ◽  
Vol 11 (7) ◽  
pp. 3554-3563 ◽  
Author(s):  
Y Wang ◽  
H P Xu ◽  
M Riggs ◽  
L Rodgers ◽  
M Wigler
Keyword(s):  
Protein Kinase ◽  
Schizosaccharomyces Pombe ◽  
Cell Shape ◽  
Single Gene ◽  
Gene Encoding ◽  
Ras Genes ◽  
Mutant Strains ◽  
Site Of Action ◽  
Partial Suppression ◽  
Normal Shape

Schizosaccharomyces pombe contains a single gene, ras1, which is a homolog of the mammalian RAS genes. ras1 is required for conjugation, sporulation, and normal cell shape. ras1 has been previously identified as ste5. We report here a gene we call byr2 that can encode a predicted protein kinase and can partially suppress defects in ras1 mutants. ras1 mutant strains expressing high levels of byr2 can sporulate competently but are still defective in conjugation and abnormally round. byr2 mutants are viable and have normal shape but are absolutely defective in conjugation and sporulation. byr2 is probably identical to ste8. In many respects, byr2 resembles the byr1 gene, another suppressor of the ras1 mutation, which has been identified previously as ste1. Our data indicate that if ras1, byr2, and byr1 act along the same pathway, then the site of action for byr2 is between the sites for ras1 and byr1.

scholarly journals The lung volume and its subdivisions in normal males

1939 ◽  
Vol 126 (845) ◽  
pp. 502-528 ◽  
Keyword(s):  
New York ◽  
Lung Volume ◽  
Preceding Paper ◽  
Sitting Posture ◽  
Total Lung Volume ◽  
South Wales ◽  
Normal Males ◽  
Male Subjects ◽  
Residual Air ◽  
Made In

A method of determining the lung volume has been described in the preceding paper (Herrald and McMichael 1938). During the course of an investigation on chronic pulmonary disease in the South Wales coalfield, sixty-six normal adult male subjects were studied as controls, and the results of this part of the investigation are here presented. The only previous work on comparable numbers was carried out in Rochester, New York, by Hurtado and his co-workers, who examined a hundred young adult normals (fifty males and fifty females) and, more recently, fifty middle-aged normal males, in the recumbent position (Hurtado and Boller 1933; Hurtado, Fray, kaltreider and Brooks 1934; Kaltreider, Fray and Hyde 1938). They also contrasted the results on males with ten subsidiary observations, made in the sitting posture, in each of the two series (Hurtado and Fray 1933 b; Kaltreider, Fray and Hyde 1938). These workers point out that no satisfactory standards of normality for total lung volume together with its subdivisions had previously been available. Their own standards would be generally acceptable were it nor for the fact that doubt has been thrown on the validity of the method used (Lassen, Cournand and Richards 1937). The source of error in the method is briefly discussed in the preceding paper, and it is shown to be most pronounced at functional residual air values of over 3.5 l. Since most normal values of this measurement are below this figure it is not surprising that our present results show remarkable general agreement with the figures of the Rochester workers. 1.Terminology Throughout this paper we use the following terminology: 2. Methods (a)Lung volume determinations The technique adopted was that described in the preceding paper. By this method the possible error of the original Christie technique is avoided.

scholarly journals byr2, a Schizosaccharomyces pombe gene encoding a protein kinase capable of partial suppression of the ras1 mutant phenotype

1991 ◽  
Vol 11 (7) ◽  
pp. 3554-3563 ◽  
Author(s):  
Y Wang ◽  
H P Xu ◽  
M Riggs ◽  
L Rodgers ◽  
M Wigler
Keyword(s):  
Protein Kinase ◽  
Schizosaccharomyces Pombe ◽  
Cell Shape ◽  
Single Gene ◽  
Gene Encoding ◽  
Ras Genes ◽  
Mutant Strains ◽  
Site Of Action ◽  
Partial Suppression ◽  
Normal Shape

Schizosaccharomyces pombe contains a single gene, ras1, which is a homolog of the mammalian RAS genes. ras1 is required for conjugation, sporulation, and normal cell shape. ras1 has been previously identified as ste5. We report here a gene we call byr2 that can encode a predicted protein kinase and can partially suppress defects in ras1 mutants. ras1 mutant strains expressing high levels of byr2 can sporulate competently but are still defective in conjugation and abnormally round. byr2 mutants are viable and have normal shape but are absolutely defective in conjugation and sporulation. byr2 is probably identical to ste8. In many respects, byr2 resembles the byr1 gene, another suppressor of the ras1 mutation, which has been identified previously as ste1. Our data indicate that if ras1, byr2, and byr1 act along the same pathway, then the site of action for byr2 is between the sites for ras1 and byr1.

scholarly journals VI. A contribution to the study of I., some of the decussating tracts of the mid- and inter-brain, and II., of the pyramidal system in the mesencephalon and bulb

1897 ◽  
Vol 188 ◽  
pp. 211-221 ◽  
Keyword(s):  
Preceding Paper ◽  
The Third ◽  
The Subject ◽  
Third Nerve ◽  
Made In

The material which furnished the subject of this research was obtained from cats in which one hemisphere had been removed, or in which a hemisection had been made in the mesencephalon through the superior corpus quadrigeminum and the third nerve. In a preceding paper I have already detailed the descending paths of degeneration, as shown by the Marchi method. In the present instance the same method is used to demonstrate certain short tract degenerations in the thalamencephalon and mesencephalon as well as the medullated fibres which leave the degenerate pyramidal system both in these regions and in the bulb.

Psychobiology of partnership behaviour

1975 ◽  
Vol 5 (4) ◽  
pp. 327-339 ◽  
Author(s):  
Detlev Ploog
Keyword(s):  
Social Behaviour ◽  
Animal Experiments ◽  
Brain Structures ◽  
Verbal Information ◽  
Social Signals ◽  
Behaviour Therapy ◽  
Species Specific ◽  
Human Social Behaviour ◽  
Made In

SynopsisAnimal experiments demonstrate that it is not only the quality of transmitted and received social signals that is important, but also their frequency and the timing of the information transmitted. In order for progress to be made in the investigation of human social behaviour and its disorders, methods must be developed which allow the transmission of verbal and non-verbal information to be measured. Experiments carried out with healthy adults and healthy and disturbed children to investigate human eye contact and distance behaviour are reported, along with experiments on the influence of gaze and body posture on spoken communication. Finally, a report on the use of behaviour therapy for an autistic child is outlined in order to explore the psychobiological correlations between social behaviour and language, which concur with extensive experiments on brain stimulation. It is suggested that there is a cerebral representation for species-specific social behaviour and a vocalization system embedded in these brain structures which is a phylogenetically patterned prerequisite for the development of human language.

scholarly journals Microtubules can bear enhanced compressive loads in living cells because of lateral reinforcement

2006 ◽  
Vol 173 (5) ◽  
pp. 733-741 ◽  
Author(s):  
Clifford P. Brangwynne ◽  
Frederick C. MacKintosh ◽  
Sanjay Kumar ◽  
Nicholas A. Geisse ◽  
Jennifer Talbot ◽  
...  
Keyword(s):  
Cell Shape ◽  
Large Scale ◽  
Living Cells ◽  
Mechanical Coupling ◽  
Compressive Loads ◽  
Structural Contribution ◽  
Cytoplasmic Microtubules ◽  
Lateral Reinforcement

Cytoskeletal microtubules have been proposed to influence cell shape and mechanics based on their ability to resist large-scale compressive forces exerted by the surrounding contractile cytoskeleton. Consistent with this, cytoplasmic microtubules are often highly curved and appear buckled because of compressive loads. However, the results of in vitro studies suggest that microtubules should buckle at much larger length scales, withstanding only exceedingly small compressive forces. This discrepancy calls into question the structural role of microtubules, and highlights our lack of quantitative knowledge of the magnitude of the forces they experience and can withstand in living cells. We show that intracellular microtubules do bear large-scale compressive loads from a variety of physiological forces, but their buckling wavelength is reduced significantly because of mechanical coupling to the surrounding elastic cytoskeleton. We quantitatively explain this behavior, and show that this coupling dramatically increases the compressive forces that microtubules can sustain, suggesting they can make a more significant structural contribution to the mechanical behavior of the cell than previously thought possible.

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